As golf balls having high spin performance on approach shots and long flight distance, two-layer structured core type or two-layer structured cover type golf balls, which comprise a center formed from soft rubber, an intermediate layer formed on the center made from a rubber or resin which is relatively harder than the center and a cover formed from a soft material, have been proposed (Japanese Patent No. 2910516, Japanese Patent Publication Nos. 239068/1997, 151225/1998, 151226/1998 and the like).
In Japanese Patent No. 2910516, a multi-piece golf ball, in which the center has a diameter of not less than 29 mm, the intermediate layer has a JIS-C hardness of not less than 85, and the specific gravity of the center is larger than that of the intermediate layer, is described. However, since the intermediate layer and cover have large thickness, the golf ball as a whole is difficult to deform at the time of hitting. Therefore, the rebound characteristics of the resulting golf ball are poor, and the flight distance when hit by a driver is not sufficiently obtained.
In Japanese Patent Kokai Publication No. 239068/1997, a three-piece solid golf ball comprising a core, an intermediate layer and a cover is described. The core has a center hardness in JIS-C hardness of not more than 75 and a surface hardness, in JIS-C hardness, of not more than 85, the surface hardness of the core is higher than the center hardness of the core by 8 to 20, the hardness of the intermediate layer, in JIS-C hardness, is higher than the surface hardness of the core by not less than 5, and the hardness of the cover, in JIS-C hardness, is lower than that of the intermediate layer by not less than 5, and the dimples occupy at least 62% of the ball surface. However, since the hardness difference between the center hardness and the surface hardness of the center is small and the spin amount at the time of hitting is large, the flight distance when hit by a driver is not sufficiently obtained.
In Japanese Patent Publication No. 151225/1998, a three-piece solid golf ball comprising a solid core, an intermediate layer and a cover is described. The specific gravity of the solid core is lower than that of the intermediate layer and the cover, the hardness of the intermediate layer is higher than that of the core, and the ball as a whole has an inertia moment of at least 83 g-cm2. In Japanese Patent Publication No. 151226/1998, a multi-piece golf ball is described, of which the center has a distortion of at least 2.5 mm under a load of 100 kg, the Shore D hardness of the intermediate layer is at least 13 degrees higher than that of the cover, and the ball as a whole has an inertia moment of at least 83 g-cm2. However, since the thickness of the intermediate layer and that of the cover are large, the golf ball as a whole is difficult to deform at the time of hitting. Therefore, the rebound characteristics of the resulting golf ball are poor, and the flight distance when hit by a driver is not sufficiently obtained.
There has been no golf ball, which is superior in flight distance and shot feel as described above.